Stanley Roberts

The preparation and characterization of titanium boride films

Abstract Metal boride films have been shown to be useful in many applications where refractory properties are required. Potential microelectronics applications include use as a diffusion barrier and as a boron diffusion source. In this study, the boron outdiffusion behavior of several compositions of titanium boride films was investigated. TiB 2.1 films did not react with the silicon substrate upon annealing up to 1092°C, but TiB films reacted with silicon at elevated temperatures, apparently to form a titanium silicide. The surface concentration of boron in the silicon substrate increased as the boron-to-titanium ratio in the boride film increased. The boron diffusivities obtained from TiB 2.1 and TiB 2.9 sources are greater than values observed for other types of boron diffusion source when analyzed with the vacancy model. Resistivity studies showed that thicker titanium diboride films had lower resistivities than thinner films when annealed above 1000°C. Post-anneal film stress was independent of anneal temperature above 900°C. The resistivity and film stress values obtained for titanium diboride films were similar to the values observed for refractory metal silicides.

The formation and characterization of rare earth boride films

Thin films of several rare earth borides were prepared by either dual-electron-beam evaporation (YB2, YB4 and YB6) or sputtering from a boride target (LaB6). Although values for bulk resistivities and work functions for rare earth borides are low (e.g.ϱ = 17 μΩ cm and o = 2.66 eV for LaB6) thin films of rare earth borides show significantly higher resistivities and work functions (ϱ = 96 μΩ cm and o = 3.8 eV for LaB6 films). Large resistivity increases were observed for rare earth boride films subjected to a 30 min steam oxidation at 1000°C. Adding silicon to the boride films allowed the film to remain conductive even after a 30 min, 1000°C steam oxidation. Also, silicon additions to LaB6 films resulted in a reduction in the film stress after a 1000°C anneal. The stresses within LaB6 and YB2 films were found to be tensile after a 30 min, 1000°C nitrogen anneal (σYB2 = 1.3 x 109 N m-2; σLaB6 = 8 x 108 N m-2). LaB6 films are shown to behave as semi-infinite diffusion sources for boron.